In the world of information technology, black hat hackers (also known as crackers or cyber-criminals) are known as the bad guys or villains. Most of them break into computers or networks without authorization to steal money and classified and sensitive information, while others are doing it simply for the challenge or the thrill of hacking. To accomplish their sinister work, crackers often create malware (malicious software) like viruses and worms to gain control of computer systems.

I have gathered here a list of ten of the most popular cyber-criminals the world has ever known. These evil geniuses were involved in high profile hacking that possibly caused millions, if not billions of dollars in total damages. However, some of them have now turned to the good side and are using their talents for the benefit of mankind.

Without further delay, here are the top 10 most infamous black hat hackers of all time:

10. Jonathan JamesAt the age of 16, Jonathan James (also known as c0mrade) became the first juvenile imprisoned for cybercrime in the United States. James carried out a series of intrusions into various systems including the computers of the Defense Threat Reduction Agency (DTRA) of the US Department of Defense. James had installed an unauthorized backdoor in a computer server in Dulles, Virginia that he used to install a sniffer allowing him to intercept over three thousand messages passing to and from DTRA employees while collecting countless usernames and passwords. This intrusion caused NASA to shut down its computers for three weeks costing them $41,000 to check and secure their systems. Jonathan James committed suicide in 2008.

9. Kevin PoulsenKevin Poulsen (also known as Dark Dante) is a notorious black hat hacker in the 1980s. One of his popular hacks was a takeover of all of the telephone lines for Los Angeles radio station KIIS-FM, assuring that he would be the 102nd caller, and the likely winner of a brand new Porsche 944. Poulsen went underground as a fugitive when the FBI started pursuing him, but was finally captured in 1991. He pleaded guilty to seven counts of mail, wire and computer fraud, money laundering, obstruction of justice, and for obtaining information on covert businesses run by the FBI. Kevin Poulsen was sentenced to 51 months in prison, which at that time was the longest sentence ever given for cracking. He is now a free man and is a senior editor at Wired News.

8. Albert GonzalezAlbert Gonzalez is a cyber-criminal accused of masterminding the biggest ATM and credit card theft in history. From 2005 through 2007, he and his group have allegedly sold more than 170 million card and ATM numbers. Gonzalez's team used SQL injection techniques to create malware backdoors on several corporate systems in order to launch packet-sniffing (specifically, ARP Spoofing) attacks, which allowed him to steal computer data from internal corporate networks. When he was arrested, authorities seized $1.6 million in cash including $1.1 million in plastic bags placed in a three-foot drum buried in his parents' backyard. Earlier this year, Gonzalez was sentenced to 20 years in federal prison.

7. Michael Calce In February 2000, Michael Calce (a.k.a. MafiaBoy) launched a series of highly publicized denial-of-service attacks against large commercial websites. His victims include Yahoo!, Amazon.com, Dell, eBay, and CNN. He hacked Yahoo! when it was still the web's leading search engine causing it to shutdown for about an hour. Calce exploited websites primarily for pride and to establish dominance for himself and his cybergroup named TNT. In 2001, the Montreal Youth Court sentenced him to eight months of open custody, one year of probation, restricted use of the Internet, and a small fine.

6. Markus HessMarkus Hess is a German hacker in the late 1980s that was recruited by the KGB and was involved in a Cold War computer espionage incident. All the way from Germany, he was able to access computer systems from the Lawrence Berkeley Laboratory (LBL) located in California. By using LBL to “piggyback” to ARPANET and MILNET, Hess attack 400 U.S. military computers including OPTIMIS Database (The Pentagon), Anniston Army Depot, U.S. Air Force (Ramstein Air Base, West Germany), Fort Buckner, Camp Foster (Okinawa, Japan). He went to trial in 1990 and was found guilty of espionage. Hess was sentenced to a one to three year prison sentence but was eventually released on probation.

5. Vladimir LevinVladimir Levin is known for his involvement in the attempt to illegally transfer 10.7 million US dollars via Citibank's computers. In 1997, Levin was brought into U.S. custody, and he admitted to only one count of conspiracy to defraud and to stealing $3.7 million. The following year, he was convicted and sentenced to three years in prison, and ordered to pay more than $200,000. Of the stolen $10.7 million, Citibank claimed that only around $400,000 had been recovered. At the moment, Levin is free and now lives in Lithuania.

4. Robert Tappan MorrisRobert Tappan Morris is an 'accidental' black hat hacker infamous for creating the first ever computer worm on the Internet known as Morris Worm. In 1988, he created the worm while he was a graduate student at Cornell University with the original aim of measuring the size of the Internet or counting the number of computers connected to it. The Morris Worm spread rapidly and infected thousands of computers. The cost of possible loss in productivity caused by the worm at each system ranged from $20,000 to more than $530,000 as estimated. Without serving jail time, Morris was sentenced to community service, probation, and a fine of $10,000. He is currently a professor at Massachusetts Institute of Technology (MIT), in the Institute's department of Electrical Engineering and Computer Science.

3. Adrian LamoAdrian Lamo is widely known for breaking into a series of high-profile computer networks that include The New York Times, Microsoft, Yahoo!, and MCI WorldCom. In 2002, he added his name to the The New York Times' internal database of expert sources and used LexisNexis account to conduct research on high-profile subjects. The Times filed a complaint, and a warrant for Lamo's arrest was issued, followed by a 15-month investigation by federal prosecutors in New York. After several days in hiding, he surrendered to the US Marshals, and then to the FBI. Lamo was ordered to pay around $65,000 in damages and was sentenced to six months house arrest at his parents' home, plus two years probation. In June 2010, Lamo disclosed the name of Bradley Manning to U.S. Army authorities as the source of the July 12, 2007 Baghdad airstrike video leak to Wikileaks. At present, he is working as a threat analyst and donates his time and skills to a Sacramento-based nonprofit organization.

2. Gary McKinnonGary McKinnon has been accused of what one US prosecutor claims is the "biggest military computer hack of all time". Between February 2001 and March 2002, he reportedly exploited 97 United States military, Department of Defense, and NASA computers. McKinnon allegedly deleted critical files from operating systems that shut down the US Army’s Military District of Washington network of 2,000 computers for 24 hours. He supposedly deleted US Navy Weapons logs, causing a naval base's network of 300 computers unusable after the September 11th terrorist attacks. McKinnon is also charged with copying of sensitive data, account files, and passwords onto his own computer. He expresses that he was only looking for evidence of free energy suppression, a cover-up of UFO activity, and other technologies that may be useful to the public. At present, McKinnon is awaiting extradition to the United States.

1. Kevin Mitnick Kevin Mitnick was once considered as the most wanted computer criminal in United States history. He was involved in a highly publicized pursuit by authorities that his misadventures were depicted in two hacker films: Takedown (a.k.a. Hackers 2) and Freedom Downtime. While he was a fugitive, he cracked dozens of computer networks and copied valuable proprietary software and stole corporate secrets from some of the largest cellular telephone and computer companies in the US. Mitnick also intercepted and stole computer passwords, altered computer networks, read private e-mails, and cloned cellular phones to hide his location. In 1999, he confessed to four counts of wire fraud, two counts of computer fraud and one count of illegally intercepting a wire communication. Mitnick was sentenced to a total of 68 months in prison and was incarcerated for 5 years that included 8 months in solitary confinement. He was released in 2000 and is now a well-known computer security consultant, public speaker, and author.